Films bearing transmissive images have become an increasingly important sector of photography, particularly in the fields of printing, semiconductor manufacturing and archival storage. In these fields, cost, processing time and image sharpness are major concerns Prior imaging methods have relied upon exposing a light-sensitive film and then developing the film using chemical developers and the like. This can be both costly, time consuming and require complicated equipment. While the present invention has application in many fields, it will be discussed with particular application in the field of printing
Printed materials are and continue to be a very important medium for disseminating information. Recent advances in computer hardware and software have made it possible for what has become known as desktop publishing. With a desktop publishing system, one can create and combine, text and graphics to form good quality printed materials at one's desk. Prior to desktop systems, one had to take their text and art work to a typesetter and graphic illustrator, who would lay-out and paste-up the work. After several processing steps, copies of the work were printed using either a printing press or a photocopier. This was often expensive and time consuming, since many of the steps were done by hand. Computers are now able to do much of that work so that one with little experience or training can put together well laid-out material. However, to make several copies of the material, an outside copy service is often needed. Indeed, if a large number of copies are needed, or if high quality or other special needs are desired, the work is sent out to a professional printshop. Color printing is often one of the special needs which requires that the work be sent out for printing.
Using color in printed materials has increased dramatically with the increased use of color computer systems. People now want color prints of color images produced by computers. Many various systems and techniques have been developed to satisfy this need for color printing.
One such system involves color separation. When a color illustration or picture is printed, all the colors in it are produced by just four inks. These are the three secondary colors: yellow, magenta and cyan; and black. Each ink is printed by a separate printing plate. Producing these plates involves two processes, color scanning and typesetting. Color scanning breaks the illustrations down into the three secondary colors and black, while typesetting converts the text into print.
A color scanner breaks down each illustration into four separate images which together will re-create the full-color picture In each separation, the picture is broken up into many separate dots. A computer in the scanner controls the size of the dots, producing larger or more numerous dots where the color must be dense and smaller or fewer dots in other parts of the separation. Breaking the picture up into dots enables the printing plate to print any color at any intensity.
Color scanning is sometimes accomplished by placing the color picture on a scanning drum. The picture, either a color transparency or piece of art work, rotates on the scanning drum. An optical system moves across the picture, detecting its color and brightness and breaking them down into a large number of dots. Signals from the optical system go to the scanner's computer where they are stored.
To produce the printing plates, either a negative or positive film is used. Using the stored signals from the scanning operation, the computer generates signals to operate a recording drum. Film is placed around the drum, which rotates. Typically a computer-controlled laser beam is used to move across the film to create four separations made of lines of dots. The yellow, magenta and cyan separations are black-and-white images formed by the amounts of each color in the original picture The black separation is an ordinary black-and-white image of the picture. The lines of dots are scanned at different angles to prevent patterns becoming visible in the printed picture After being imaged by the laser beam the film is developed, fixed, washed and dried.
To make a printing plate of the black separation, a plate is coated with a light-sensitive substance. Light is shown through the combined films of the text and the black separation to expose the plate, which is then developed so that the text and picture form in the coating. The plate is then treated with chemicals, which penetrate parts of the coating and create the text characters and picture dots on the plate. The kind of chemical treatment depends on whether the plate is for letter press, gravure or litho printing. Three more printing plates are then made from the other color separations in the same way. Therefore, each page that is to be printed in color requires at least four different sheets of imaged film. Once made the printing plates may then be used in a printing press to produce high quality copies of the material.
While systems of this type produce high quality material, the expense of such systems can be more than most desktop publishers can reasonably afford. Therefore, a significant amount of color print work continues to be sent out to outside printshops. Indeed, filling the increasing demand for color printing has become a highly competitive field, so that even small cost advantages are of major import. Another important consideration is the speed at which a system prints. Thus, reducing the processing time in a printing system is important.
Therefore, it is an object of the present invention to design a system and method for producing high contrast, instant transparent images.
It is another object of the present invention to reduce the cost of printing systems and their operating expenses.
It is yet another object of the present invention to simplify the steps required to produce either a negative or positive film used to make a printing plate.